title: Complement-induced solubilization of C-reactive protein-pneumococcal C-polysaccharide precipitates: evidence for covalent binding of complement proteins to C-reactive protein and to pneumococcal C-polysaccharide.
abstract: Insoluble precipitates between C-reactive protein and pneumococcal C-polysaccharide were solubilized by fresh but not heat-inactivated human serum. Solubilization was dependent on the C-reactive protein to C-polysaccharide ratio and the serum concentration and proceeded optimally at 37 degrees C. On 12 to 30% sucrose density gradients solubilized complexes sedimented as a broad peak between the 7S region and the bottom of the tube. In C2-deficient human serum, solubilization was delayed by 30 min and then proceeded at a slow rate. Immunoprecipitation experiments indicated that C3, C4, C5, and to a lesser extent C1q were deposited on solubilized complexes. After dissociating solubilized complexes with EDTA, a considerable percentage of C-polysaccharide coprecipitated with C3, C4, and C5, whereas C-reactive protein coprecipitated with only C3. SDS-PAGE analysis of solubilized precipitates indicated the formation of covalent complexes between fragments of C3 and both C-polysaccharide and C-reactive protein.
mesh_terms: D002097:C-Reactive Protein / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002499:Centrifugation, Density Gradient; D011232:Chemical Precipitation; D003175:Complement C2 / Q000378:metabolism; D003165:Complement System Proteins / Q000378:metabolism*; D004492:Edetic Acid / Q000494:pharmacology; D006801:Humans; D009194:Myeloma Proteins / Q000276:immunology; D011135:Polysaccharides, Bacterial / Q000276:immunology / Q000378:metabolism*; D011951:Receptors, Complement; D012995:Solubility; D013296:Streptococcus pneumoniae / Q000276:immunology*
chemical_list: D003175:Complement C2; D009194:Myeloma Proteins; D011135:Polysaccharides, Bacterial; D011951:Receptors, Complement; D003165:Complement System Proteins; D002097:C-Reactive Protein; D004492:Edetic Acid; D002118:Calcium